Pediatric Short Bowel Syndrome AbdulAziz Al-Gain Abdullah Al-Rashed Abdulrahman Arafah A

Definition There are numerous definitions for short-bowel syndrome (SBS). The simplest definition is that there is inadequate intestine to maintain normal nutrition by eating. State of malabsorption and malnutrition that occurs following massive anatomical or functional loss of the small intestine.

Definition Overall, patient with 30 cm or more of small bowel are more likely to survive on enteral nutrition, whereas with less than 30 cm they are more likely to need parenteral nutrition.

Because infants and children require increased calories to grow and develop, SBS can have a more devastating effect in these patients Before the availability of total parenteral nutrition (TPN, food delivered into the veins), most infants and children with SBS died from malnutrition.

Etiology The majority of SBS involves anatomical loss of segments of the small intestine caused by surgical resection. Functional loss, as seen in severe Hirschsprung's disease, is a state of decreased motility and resultant decreased absorption.

Etiology The etiology of SBS can be congenital or postnatal in origin. Congenital causes of SBS include : midgut volvulus, Gastroschisis, and omphalocele; superior mesenteric artery deformities such as "apple-peel" or "Christmas tree" deformities;

Etiology Continue Congenital causes : intestinal atresias; Aganglionosis (Hirschsprung's disease).

Etiology Postnatal causes include: necrotizing enterocolitis (NEC) Malrotation may result in volvulus with bowel resection secondary to ischemic injury. Intestinal resection secondary to Crohn disease, trauma, pseudo-obstruction syndrome Trauma

Necrotizing enterocolitis and midgut volvulus from malrotation are the two most common causes of SBS. Necrotizing enterocolitismidgut volvulus from malrotation

Normal physiology & Pathophysiology

The small intestine is completely formed by 20 weeks’ gestation. Most of its growth prior to birth occurs in the third trimester. Before 27 weeks’ gestation, the average length of the small intestine is 115 cm.

This length increases to approximately 250 cm with a diameter of 1.5 cm after 35 weeks’ gestation. In contrast, the adult intestine is 600 to 800 cm in length and 4 cm in diameter. The mucosal surface area increases with age. Infants have 950 cm2; adults have 7500 cm2.

Nutrients, vitamin B12, calcium, iron, and bile acids are absorbed through the cells of this lining. Mucus covers the surface of the mucosa cells and acts as a trap to hold nutrients in contact with the cell surface. Mucus also acts as a bacterial barrier.

The most crucial factor is the length of the remaining intestine. Removal of the stomach, jejunum, or colon is better tolerated than removal of the ileum

The stomach digests nutrients by the action of acid and enzymes and produces “intrinsic factor,” which is essential for vitamin B12 absorption. The stomach reacts to massive loss of intestine by secreting large volumes of high acid–containing stomach juices at least for a time.

The jejunum is the site of absorption of most nutrients and minerals, such as calcium, magnesium, and iron. With removal of the jejunum, there is loss of some of the enzymes that break down sugars, which decreases sugar absorption.

Unfortunately, bacteria can use these unabsorbed sugars and produce lactic acid. The absorption of the increased lactic acid can lead to increased acid in the bloodstream

Fat and protein digestion may be reduced if the jejunum is gone. Calcium and magnesium losses are increased

Carbohydrate, protein, fluid, and electrolytes are also absorbed in the ileum. The ileum is the principal source of absorption of bile acids; vitamin B12; and the fat- soluble vitamins A, D, E, and K. Removal of most of the ileum results in vitamin B12 and fat-soluble vitamin deficiencies and diarrhea.

The diarrhea is from both the large volume of fluid passed into the colon (large intestine), and the unabsorbed bile salts can cause the colon to release water. Loss of these bile salts can also result in a decrease in fat absorption since the bile salts help the intestine to absorb fats.

The ileocecal valve slows the progress of intestinal fluids into the colon. It also increases the pressure gradient between the ileum and the colon to prevent the colon fluids with high concentrations of bacteria from moving back up into the small intestine.

Removal of the large intestine has minimal effect on digestion and absorption. The colon is the site of absorption of fluid and sodium and the excretion of potassium and bicarbonate. In SBS, the presence of the colon is of value because it increases the absorption of fluids and electrolytes and decreases diarrhea

Short Bowel Syndrome - pathophysiology in points Markedly decreased mucosal surface area due to resection Loss of trophic hormones Loss of peptide hormones that regulate motility Abnormal transit Malabsorption of protein, fat, carbohydrate, vitamins, electrolytes, and trace elements, depending on site of resected intestine.

Short Bowel Syndrome - pathophysiology in points Bowel adaptation can occur over time. Increased surface area due to bowel dilatation, villus hypertrophy, and bowel lengthening can occur. Stimulation of luminal contents is needed for bowel growth and factors such as glutamine, short-chain fatty acids, tropic hormones, and growth factors may be important for bowel growth.

Short Bowel Syndrome - pathophysiology in points The patient can lose as much as half of the intestine if the duodenum, distal ileum, and ileocecal valve (ICV) are present. If the ICV is gone, patients may not be able to tolerate even a 25% loss of intestine without the help of total parenteral nutrition (TPN). Normal bowel length: 150–200 cm (26 weeks’ gestation); 200–300 cm (at birth in full-term infant); 600–800 cm (adult)

Short Bowel Syndrome - pathophysiology in points Infants have no intestinal reserve and do not tolerate small-bowel resection as well as do adults. However, long-term prognosis may be better because of hypertrophy and hyperplasia of the intestine. Gastric acid hypersecretion occurs soon after intestinal resection, but is transient.

Adaptation of the Intestine ✓ Loss of a significant amount of the small intestine produces changes in the bowel result is an increase in the intestinal surface area of the inside lining (mucosa) of the intestine and an increase in absorption and digestion. ✓ The inside lining of the intestine is made of strands of mucosa (villi) that increase the surface area

Adaptation of the Intestine ✓ The first and most significant adaptive change is an increase in growth of the villi. ✓ The villi are longer and thicker. The inside diameter of the intestine also increases. ✓ Resulting in an increase in water and electrolyte absorption.

Adaptation of the Intestine ✓ Providing enough calories to support growth and development is important. ✓ The villi get smaller in patients getting calories only from TPN exclusively. ✓ This condition can be reversed by feeding small amounts of nutrition into the stomach or intestines, typically referred to as trophic feeds.

Management of Short Bowel Syndrome

✓ In the early period after intestinal loss, attention is directed toward keeping the fluids and electrolytes in the body normal. ✓ TPN is begun. ✓ Balanced solutions of protein, glucose, and fat should be administered. ✓ Prophylactic measures to prevent PN-induced liver damage should be instituted (e.g., prevention of overfeeding, early introduction of enteral feeds, cycling of PN when patient is stable). If cholestasis is present, it is necessary to modify amount of trace elements in PN.

✓ Need permanent central access to deliver concentrated PN solutions. ✓ Excess secretions, which are lost through stomas or diarrhea, must be replaced. ✓ Blood levels of calcium, magnesium, trace elements, and vitamins and blood pH (acid) must be monitored. ✓ Fat (40% of calories) is given into the bloodstream daily or at least three times per week.

✓ As soon as GI function has returned, intestinal feeds are introduced gradually. ✓ This is usually accomplished through a gastrostomy or nasogastric tube. ✓ Infants and young children must be fed at least in part orally, however, to establish their ability to suck and eat. ✓ Because adaptation begins early after loss of intestine, small amounts of feeds are started early to stimulate adaption of the intestine. ✓ Small volumes of liquid feedings are introduced first.

Use of elemental diets (where all the nutrients are broken down into simplified forms that can be easily absorbed) have become increasingly popular to feed patients with SBS. These diets have the advantage of being better absorbed. However, more complex diets are more trophic (promoting growth) to the GI tract and help increase adaptation. The decision to use one formula over the other depends on each individual child.

✓ Most diets that are well-tolerated with SBS contain peptides as the major protein source and forms of glucose as the sugar source. ✓ Long-chain triglycerides and short-chain fatty acids are important and should be added gradually to the diet because they stimulate mucosal growth. In the past, patients were not fed complex fats because of the fear of increasing diarrhea. ✓ Several clinical studies have shown that this is incorrect. One type of fat, medium-chain triglycerides, are absorbed readily through the intestine.

✓ The volume and complexity of feedings are increased gradually. ✓ Consideration should be given to adding fiber to the diet, particularly pectin. ✓ Vitamins B12, A, D, E, and K may be required. ✓ As more nutrients are absorbed, the amount of TPN that is given is decreased. ✓ During hospitalization and at home, stools should be monitored periodically for reducing substances which indicate that sugars are not being absorbed, amount of water, frequency of stools, volume, and the presence of undigested fat.

MEDICATIONS Supplementation of vitamin (E, D, K, B 12, folic acid) deficiency, calcium, magnesium, iron, and zinc H 2 -receptor antagonists and proton pump inhibitors decrease gastric acid hypersecretion and reduce gastric secretory volume. Antidiarrheal drugs: Codeine, diphenoxylate, and anticholinergic drugs (e.g., loperamide) to decrease motility (caution in patients with slow transit or bacterial overgrowth).

Ion-exchange resins:Cholestyramine binds intraluminal dihydroxy bile acids to prevent bile acid-induced diarrhea. Octreotide/Somatostatin: Decreases gastric, pancreatic, and intestinal secretions; slows gastrointestinal motility and splanchnic blood flow Bacterial overgrowth: Commonly used oral antibiotics are metronidazole, trimethoprim- sulfamethoxazole, vancomycin, andgentamicin. Prokinetic agents: Reglan to treat delayed gastric emptying MEDICATIONS

Miscellaneous: Sucralfate to treat bile reflux, probiotics to treat bacterial overgrowth, Ursodiol for cholestasis, Polycitra for electrolyte losses, dietary fiber to enhance absorption-caution in infancy. Duration of treatment: Depends on amount and site of bowel resected and degree of intestinal adaptation that occurs. The more the resection, the longer is the therapy. Successful enteral feeds decrease the duration of PN. Macronutrient losses decrease with intestinal adaptation. Micronutrient supple

surgery Surgery is useful in patients who develop strictures and partial obstruction or in those who have very short intestine length. Intestinal interpositions (isoperistaltic or antiperistaltic) can be used to delay gastric emptying, slow intestinal transit, and increase absorption, intestinal valves, and reversed intestinal segments. Intestinal lengthening and tapering procedures, including the Bianchi and step enteroplasty procedures, increase absorptive surface area. In patients with extremely short intestines and PN dependency, small- bowel transplantation or small-bowel/liver transplantation is considered.

The Biarchi procedure for making the intestine longer. The enlarged, dilated intestine is divided down the middle after the blood vessels feeding it are separated to one side or the other. The ends are then hooked up. The enlarged intestine now becomes longer and fairly normal

The STEP procedure. A staple which divides the intestine after stapling either side is used to make an “accordion” of the intestine that makes it longer and a fairly normal size.

FOLLOW UP

prognosis Depends on site and amount of bowel resected The greater the amount of bowel resected, the worse is the prognosis. Loss of ICV portends a worse prognosis. Loss of jejunum and ileum creates a poorer clinical condition than loss of colon. The longer it takes to tolerate full enteral feeds in a patient, the worse is the prognosis. Most progress is made in the first year after bowel resection. Development of severe TPN liver disease: Poor prognosis

complications Fluid and electrolyte loss, resulting in diarrhea, dehydration, and metabolic acidosis Calcium and magnesium deficiency, resulting in bone disease and osteoporosis Carbohydrate malabsorption Fat malabsorption Vitamin A deficiency: Increased susceptibility to infections Vitamin D deficiency: Bone disease (e.g., rickets) Vitamin E deficiency: Peripheral neuropathy, hemolysis Vitamin K deficiency: Prolonged clotting time, bruising Vitamin B

complications Folic acid: Macrocytic anemia Gallstones: Due to disturbed enterohepatic circulation of bile salts and lithogenic bile formation Renal stones: Due to fat malabsorption and increased oxalate absorption Failure to thrive TPN-dependent liver disease: Cholestasis, end stage is cirrhosis and portal hypertension Zinc deficiency: Poor growth, infections Carnitine deficiency: Contributes to development of steatosis Sepsis Small bowel bacterial overgrowth and D-lactic acidosis due to stasis, causing encephalopathy, ataxia, and other neurologic symptoms

patient-monitoring Signs to watch for: ◦ Vomiting, diarrhea, weight loss, severe fluid and electrolyte abnormalities, sepsis, bowel dilatation, intestinal obstruction ◦ Major cause of death: Sepsis and cholestatic liver disease

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